Recently, there has been growing interest in energy storage technologies. As the application fields of energy storage technologies have been extended to mobile phones, camcorders, laptop computers and even electric cars, efforts have increasingly been made towards the research and development of electrochemical devices. In this aspect, electrochemical devices have attracted the most attention. Among them, the development of rechargeable secondary batteries has been the focus of particular interest. In recent years, extensive research and development has been conducted to design new electrodes and batteries for the purpose of improving capacity density and specific energy of the batteries.
Among currently available secondary batteries, lithium secondary batteries developed in the early 1990's have received a great deal of attention due to their advantages of higher operating voltages and much higher energy densities than traditional batteries using aqueous electrolyte solutions, such as Ni-MH batteries, Ni—Cd batteries, H2SO4—Pb batteries, and the like.
Generally, a lithium secondary battery is designed such that a stack or fold structure of a unit cell consisting of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is embedded in a battery case made of a metal can or a laminate sheet into which an electrolyte solution is then injected or poured.
The electrode assembly of positive electrode/separator/negative electrode structure constituting the secondary battery is greatly classified into a jellyroll-type (fold-type) electrode assembly and a stack-type electrode assembly based on its structure. The fold-type electrode assembly (jellyroll) is manufactured by folding long sheet-type positive and negative electrodes coated with active materials with a separator interposed between the positive electrode and the negative electrode, and the stack-type electrode assembly is manufactured by stacking a plurality of positive electrodes and negative electrodes with a predetermined size in a sequential order with separators interposed between the positive electrodes and the negative electrodes. The jellyroll-type electrode assembly has advantages of being easy to manufacture and high energy density per weight.
A secondary battery with the jellyroll-type electrode assembly experiences damage of the separator resulting from not only contraction of the separator by heat generated from an electrode tab, particularly, a negative electrode tab, during high-rate discharge, but also adhesion of the electrode active material and the separator in semi-melting state. As a result, there is high likelihood that a short circuit will occur due to a contact between the negative electrode and the positive electrode in the jellyroll-type electrode assembly.
Accordingly, to solve the problem, there is still a need for development for a jellyroll-type electrode assembly with improved stability for preventing a short circuit between a positive electrode and a negative electrode caused by heat generated from an electrode tab and a secondary battery comprising the same.